Process and arrangement for starting reactor for reaction of ferrosilicon with gaseous halogenation agent

ABSTRACT

The reaction of ferrosilicon with a gaseous halogenation agent is started by flowing a protective gas upwardly through a ferrosilicon charge on a grate, conducting an electric current through the charge at least until a temperature of 200* C. is reached and then replacing the protective gas by the halogenation agent, e.g., hydrogen chloride gas, and stopping the flow of electric current as soon as the exothermic reaction is selfsustaining. An apparatus for carrying out this process is also disclosed.

United States Patent Vollbrecht Y [451 Nov. 7, 1972 [s41 PROCESS ANDARRANGEMENT FOR [56] References Cited STARTING REACTOR FOR REACTION 0FFERROSILICON WITH GASEOUS UNTED STATES PATENTS HALOGENATION AGENT3,161,501 12/1964 Southam ..l3/23 X [72] Inventor: nehmkudlgervonbrecht, Rheinfeb 3,448,973 6/ 1969 Derham ..l3/23 X den/Baden GermanyPrimary Examiner-Roy N. Envall, Jr.

1731 'Assignee: Deutach Gold-und'Sllber-Schudeanflrwmeyecushmanevarbwcushman stalt vormals Roessler, Frankfurt (Main), Germany 7]ABSTRACT [221' Filed; March 19 1971 'ljhe reaction of ferrosilicon witha gaseous halogenatron agent is started by flowing a protective gas up-PP 125,938 wardly through a ferrosilicon charge on a grate,conducting'an electric current through the charge at least until atemperature of 200 C. is reached and then IS/Q3, 23/205 rcplacingltheprotective gas by the halogenation agent, I! n 051) 3/60 cg" hydrogenchloride gas and Stopping the flow of [58] F'eld Search 263/77" 205electric current as soon as the exothermic reaction is self-sustaining.An apparatus for carrying out this process is'also disclosed.

6 Claims, 1 Drawing Figure i 1 PROCESS AND. ARRANGEMENT FOR STARTINGREACTOR FOR REACTION OF FERROSILICON WITH GASEOUS IIALOGENATION AGENTe.g., silicochlor'oform, silicobromoform, silicofluoroform,silicoiodoform, dichlorosilane, dibromosilane, imonochlorosilane andmonobromosilane are valuablestarting materials for the production of thesilicon electronic grade, organo silicon compounds, pyrogenic silica,water repellant agents, etc. They'can be produced by reaction of siliconor silicon alloys with gaseous halogens, e.g., chlorine, bromine,;iodineor'fluorine, or hydrogen halides at temperatures about 200 C. orabove,at temperatures up to 1,500" C. t I

According to a known process the required silicon tetrachloride'for therecovery of pyrogenic silica was produced by the reaction of -89 to 91percent siliconcontaining ferrosilicon with hydrogen chloride attemperatures of about 800 to l,200 C. The reaction can be carried outcontinuously, for example, by charging from above with ferrosiliconlumps a closed reactor, circular in cross section, the reactor having avibratory grate in its lower part. In the vicinity of the grate thereare gas inlet conduits. A charging arrangement for ferrosilicon, as wellas an exit conduit for the gaseous reaction products are located on theupper side of the reactor. Hydrogen chloride is led from below throughthe FeSi charge on the grate while discharging the ash formed in theexothermic halogenation reaction 'by vibrating the grate and drawing offthe volatile halogenation products from the upper section of thereactor.

According to known starting processes the starting of the reactor occurswhile a slender charge, e.g., about 250 mm. high, of ferrosilicon lumps,(e.g., grains of 80-150 mm.) is heated with the help of a hydrogen orcreased slowlyup to'the amount required for complete operation since atoo quick increase of the amount fed regularly causes a cooling of thepreheated starting layer below the starting temperature of the reaction.

On the other hand, if one proceeds with a thicker ferrosilicon layer,then the preheating coalwa'rms the upper part of this layer to such anextent that this reacts to completion and the reaction spreads to theferrosil: icon further added from above; the lumpy material which isunderneath this starting layer remains preponderantly withdrawn from thereaction and blocks the grate because the reaction zone practicallycannot spread against the gaseous reactants introduced from below thegrate. v

The necessary time until reaching full operation in the customarypreheating process is considerable and in reactors with an. hourlythroughput of 100 kg. of ferrosilicon in the most favorable case amountto about 48 hours.

- The invention is based on the problem of substituting a processforthis expensive, time-consuming and additionally, still unsafe startingprocedure for reactors for the reaction of ferrosilicon with gaseoushalogenation agents. The process should produce, in a simple manner, aquick and reliable preheating of a vibratory grate reactor prefilledwith a complete FeSi charge. A further problem is in the development ofa suitable apparatus means for carrying out the process.

oil burner to a temperature at which the exothermic reaction between thegaseous halogenation agent and ferrosilicon starts while the burner ismounted sideways on the reactor and the flame is allowed to sweep overthe charge. This has the disadvantage that the steam occurring as aresult of the oxidation of the fuel partially condenses in the region ofthe reactor and forms liquid acid .with the subsequently addedhalogenation agent. This acid 'corrodes the reactor and besides,

brings about silicification. A further disadvantage is that in soot-freeburning of oil excess oxygen has to be used. In doing so, oxidation ofthe ferrosilicon surface easily occurs and thereby causes difficultiesin the subsequenthalogenation reaction. To avoid these disad-- vantagesit has already been tried to bring the ferr'osil icon to the necessarytemperature by placing glowing charcoal thereon. Two difficulties arethereby encountered. If a good, thoroughly heatable, thin ferrosiliconlayer is to be obtained the ferrosilicon added to the The first problemis solved according to the invention by a process consisting of flushinga charge of ferrosilicon lumps from below with a protective gas andalso, at a downwards flowing place inside the charge, at least in aplace near the grate, leading an electrical current through atleast aportion of the cross section of the charge until the current flowingregion of the charge has reached a temperature of atleast 200 C.Thereupon the protective gas is either immediately, or graduallyreplaced by the gaseous halogenation agent and the current supplystopped assoon as the addition of the gaseous halogenation agentsuffices to maintain the exothermic reaction in-motion. The current flowcan be supplied up to a' maximum temperature of 1.500c.

Any ofthe halogens or halogen halides mentioned previously can be usedas the halogenation agent.

According to apret'erred form of the process of the invention, theprotective gas is replaced byhydrogen chloride gas at a temperature ofthe current flowing region of the charge between about 600 C. and 900C., preferably about 800 C.

As protective gases it is possible to use an inert gas,

preferably inert gases such as nitrogen. Other inert formed in thecharge from which the reaction can progress quickly. The proportioningof the space is arranged according to the characteristics of the powersource, it is empirically adjusted by this.

The temperature in the area of the charge where the current is flowingis best measured by a thermocouple reactor after the start of thereaction can only be inelement in a thermal protective tube.

. The second problem on which the invention is based is solved by anarrangement for carrying out the process of the. invention. Thisconsists of. a known closed reactor, circular in cross-section, andprovided with a vibratory grate in its lower portion. Below the gratethe'reactor has gas inlet conduitsand on its upper side there is acharging arrangement for ferrosilicon as well as an exit conduit for thegaseous reaction products. The arrangement, according to the device, ischaracterized by at least two wall ducts arranged above the grate in thereactor jacket, at least two of which are arranged near by the grate.

Through .these wall openings insulated electrodes of conductivematerials are led into the reactor, as well as at least one thermocouplein a thermal protective tube to the side of the ideal connecting line ofopposite polar electrodes, preferably arranged near the grate.

Among others, electrodes of iron rods, tapered to a point in front, forexample, of about 20 mm. diameter have shown good results. Theirinsulation against the metal jacket of the reactor can take place in anespecially simple development of the invention by a wrapping of anasbestos ribbon in the area of their passage through the reactor jacket.

An especially trouble-proof and sufficiently exact measurement oftemperature evolving in the area of the charge in which the electriccurrent flows is made possible when the thermocouple is arranged about20 cm. to the side of the ideal connecting lineof two opposite polarelectrodes.

The arrangement of the apparatus and the carrying out of the process ofthe invention will be further explained with the aid of the accompanyingdrawing and an illustrative example.

The single FIGURE of the drawing is a schematic illustration of theapparatus of the invention.

' The abbreviation Nm /h means Normal cubic meters per hour, i.e., thecubic meters per hour at standard temperature and pressure.

EXAMPLE As shown in the drawings the apparatus consists of a closedreactor 1, circular in cross-section, which is proyided with a vibratorygrate 2, in its lower portion and Process for Vibratory Grate Reactorscorresponding a conduit 4, for ferrosilicon as well as an exit conduit5,

for the gaseous reaction product. About 15 cm. above the grate arefound, on opposite walls of the reactor, two wall openings 6 and 16.Through these openings the electrodes, 7 and 17, are carried into thereactor.

ter, tapered to a point in front. There is a distance of about 400 mm.between the points of the electrodes. They are electrically insulatedagainst the wall openings, 6 and 16, by means of wrappings, 8 and 18, ofan asbestos ribbon.

, The electrodes consist of iron rods, 20 mm. in diame- In the upperthird of the charge there is analogously installed a correspondingelectrode pair, 27 and 37. The opposite electrodes are connected withthe'poles of a power source, 9 (welding transformer). A thermocouple,10, which is located in a thermal protective tube (not shown), isconducted from below between the bars of the grate about -20 mm. abovethe grate level. The heatsensitive part of the thermocouple is foundabout 13 cm. to the side of the ideal connecting line of the electrodes,7 and 17, near'the grate. The thermocouple, 10, is connected with atemperature indicating apparatus, 1 1.

The reactor containing the lumps of the ferrosilicon charge at the startofthe operation is first flushed from below through gas inlet conduit,3, with about 50 Nm lh of nitrogen. Thenthere is. applied to theelectrodes a voltage of about 60 volts anda current of about 250 A. andthe temperature observed on the in-, dicating instrument. After reachinga temperature of about 800 C. the flow of nitrogen is replaced by ahydrogen chloride gas flow of about 40 Nm lh, which then is increasedwith rising temperature to the amount intended for operation, namely300. Ntn lh. Over the entire cross-section and over theen'tire height ofthe charge there is gradually developed a hot reaction zone of about1,l00 C. whereupon the starting device of the furnace is shut off.Thereupon the electrodes, 7, 17, 27 and 37 are removed from the reactorand the'wall openings, 6, 16, 26and 36, closed.

What is claimed is:

1. An apparatus for starting the reaction of a charge of ferrosiliconwith a gaseous halogenation agent, said apparatus comprising a reactor,circular in cross-section, a vibratory grate in the lower portion of thereactor for holding a ferrosilicon charge, a gas inlet conduit below thegrate, a conduit for charging ferrosilicon in the upper part of thereactor, a gaseous product exit conduit in the upper portion of thereactor, at least two openings in the reactor wall above the grate, atleast two of said wall openings being near said grate, electrodes ofelectrically conductive material extending into said reactor throughsaid wall openings and insulated from saidwalls, said two electrodesnear said grate being connected to opposite poles of a source ofelectrical power, the ends of said electrodes within the reactor nearthe reactor grate determining an ideal connecting line of the oppositepolar electrodes, and a protected thermocouple to the side of said idealconnecting line.

2. An apparatus according to claim 1 wherein the thermocouple is nearthe grate and the two electrodes near the grate are positioned onopposite sides of the wall.

3. An apparatus according to claim 1 wherein the electrodes are ironrods of about 20 mm. diameter and pointed in the front.

4. An apparatus according to claim 1 wherein the. electrodes areinsulated from the reactor wall by an asbestos covering.

5. An apparatus according to claim 1 wherein the thermocouple is located10 to 20 cm. on the side of said ideal connecting line.

6. An apparatus according to claim 5 wherein there is provided a secondpair of electrodes extending into said reactor above said two electrodesnear said grate and said thermocouple is connected to a temperatureindicating means.

2. An apparatus according to claim 1 wherein the thermocouple is nearthe grate and the two electrodes near the grate are positioned onopposite sides of the wall.
 3. An apparatus according to claim 1 whereinthe electrodes are iron rods of about 20 mm. diameter and pointed in thefront.
 4. An apparatus according to claim 1 wherein the electrodes areinsulated from the reactor wall by an asbestos covering.
 5. An apparatusaccording to claim 1 wherein the thermocouple is located 10 to 20 cm. onthe side of said ideal connecting line.
 6. An apparatus according toclaim 5 wherein there is provided a second pair of electrodes extendinginto said reactor above said two electrodes near said grate and saidthermocouple is connected to a temperature indicating means.